System for detecting a leakage in an intake line of an internal combustion engine

ABSTRACT

A system for detecting a leakage/failure in in an intake line of an internal combustion engine comprising an intake line (IL) and an exhaust line (EL), means (HFM) for measuring or for estimating a quantity of fresh air ({dot over (m)} HFM ) entering said intake line (IL), means for measuring or for estimating a quantity of fuel ({dot over (m)} FUEL ) injected in the engine (E), measurement or estimation means (λ and/or NOx), on the exhaust line, adapted to provide a first value (λ measured ) of an air/fuel ratio introduced in the internal combustion engine (E), the system comprising processing means (ECU) adapted to calculate a second value (λ exp ) of said air/fuel ratio, calculated on the basis of the measured and estimated quantities of fresh air ({dot over (m)} HFM ) and fuel ({dot over (m)} FUEL ) to calculate an error (λ err ) between the first and the second value (λ measured −λ exp ) and to detect a condition of leakage/failure if said error is outside a predefined interval [λ err −, λ err +] containing the value zero.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Italian Patent ApplicationNo. MI2013A001571 filed Sep. 24, 2013, the entirety of the disclosuresof which are expressly incorporated herein by reference.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable.

APPLICATION FIELD OF THE INVENTION

The present invention refers to the field of the internal combustionengines equipped with at least one low-pressure exhaust gasrecirculation duct and more precisely to a system for detecting aleakage in an air intake line and/or EGR of an internal combustionengine.

DESCRIPTION OF THE PRIOR ART

The emission regulations for internal combustion engines requirestricter and stricter emission limits and more and more demandinghomologation cycles. One of the pollutants which has the highest impactand which the regulations require to keep under control is NitrogenOxide (NOx): the EGR (Exhaust Gas Recirculation) is the system in chargeof, in most applications, the reduction of such pollutant.

A possible failure lies in the intake of fresh air in the low-pressureEGR duct. In other words, fresh air is introduced instead ofrecirculating exhaust gas. Thus, on the one hand, the performance, interms of power/torque delivered by the internal combustion engine,improves, but on the other hand, it is no longer possible to properlycontrol/limit the NOx emissions.

Such type of failure may occur essentially for two reasons: anaccidental breaking of the low-pressure EGR duct or a deliberate openingperformed by the driver, in order to increase the performance of theinternal combustion engine.

Another anomalous conditions that may occur is provoked by a damage ofthe intake duct, for example due to a cracking.

US20120143459 shows a method to detect possible leakages in alow-pressure EGR system. The present description will include in thefollowing a direct comparison between such method and the presentinvention.

SUMMARY OF THE INVENTION

Therefore the aim of the present invention is to provide a system thatis able to monitor the possible intake of fresh air in/through thelow-pressure EGR duct and/or in an intake line of an internal combustionengine, preferably supercharged.

The object of the present invention is a system for detecting a leakagein an intake line of an internal combustion engine.

“Intake line” has to be intended as any duct connected with the intakemanifold of an internal combustion engine, including the portions of therecirculation branches EGR downstream of the respective valves—accordingto the circulation direction of the exhaust gases—, the respective EGRvalves and including superchargers, possibly present if the scheme issupercharged.

Advantageously, according to the present invention, it is possible,depending on the type of scheme implemented, to identify one or moresegments affected by the leakage.

An internal combustion engine comprising the aforementioned system, avehicle or a fixed apparatus implementing the aforementioned system arealso object of the present invention.

Another object of the present invention is a method for detecting aleakage in an intake line of an internal combustion engine.

The claims describe preferred alternative embodiments of the invention,and are an integral part of the present description.

BRIEF DESCRIPTION OF THE FIGURES

Further purposes and advantages of the present invention will becomeclear from the following detailed description of a preferred embodiment(and of its alternative embodiments) and the drawings that are attachedhereto, which are merely illustrative and non-limitative, in which:

FIG. 1 shows a general diagram of an internal combustion enginecomprising a low-pressure EGR duct wherein the system that is object ofpresent invention is implemented;

FIG. 2 shows an illustrative scheme comprising both a low-pressure EGRduct and a high-pressure EGR duct, wherein each portion of the differentducts is numbered. In the figures the same reference numbers and lettersidentify the same elements or components.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

With reference to FIGS. 1 and 2, an internal combustion engine E,preferably of the diesel cycle type, with any number of cylinders, forexample 4 or 6, is equipped with an intake manifold IP connected withthe outlet of the supercharger or a turbo-supercharging unit TC. Theinlet of such supercharger C is connected to the intake filter box Fthrough the duct FC.

Between the intake filter box F and the connection point between theduct EL and the duct FC, a mass flow measuring device (HFM) is arranged,generally present on the internal combustion engines.

As it will be clear in the following, the presence of theturbo-supercharger unit is optional.

The inlet of the turbine T of the same unit TC is connected to theexhaust manifold EP and the outlet is connected to an exhaust gaspost-treatment system ATS.

A low-pressure EGR duct EL is connected between the outlet of theturbine T or the exhaust gas treatment system (ATS) and the inlet of thesupercharger C. A valve ELV is arranged on any point of such duct EL,for example on the outlet point of the duct FC, to regulate the quantityof exhaust gas to be recirculated.

For the purposes of the present invention, a low-pressure EGR duct canbe also an EGR duct of an aspirated engine, namely without superchargingunits.

The concept of low pressure, in this context, is clear in relation tothe fact that exhaust gas are withdrawn downstream of the turbine T.

The internal combustion engine, if supercharged, can be optionallyequipped with a high-pressure EGR duct EH, connected between the exhaustmanifold EP and the intake manifold IP, thus upstream of the inlet ofthe turbine T and downstream of the outlet of the supercharger C. Aregulation valve EHV is arranged in any point of such duct EH, forexample in the outlet point of such duct in the intake manifold IP, orin the connection point between such duct EH and the exhaust manifoldEP, to regulate the quantity of high-pressure EGR gas to berecirculated.

In FIG. 1, the low-pressure recirculation duct EL is shown asinterrupted by the superimposition of a block AF having the label {dotover (m)}_(AirFault) which ideally represents a leakage on thelow-pressure EGR duct EL which allows the intake of fresh air in theengine E through the low-pressure EGR valve ELV. Such fresh air is nottaken into account by the device for measuring the mass flow (HFM).

As it will be made clear in the following, the intake of fresh air maytake place also along the duct FC comprised between the device formeasuring the mass flow (HFM) and the inlet of the supercharger C ifpresent, or in any point downstream of the device for measuring the massflow (HFM) in case the engine is not equipped with any supercharger.

The engine E is also equipped with a fuel injection system IS (not shownin FIG. 2) which comprises means for measuring or for estimating thequantity of fuel injected in the cylinders.

In FIG. 2, the thick lines identify the portions of the intake line towhich the present invention is applied. It is immediately evident thatfor the low-pressure EGR duct it is possible to detect a leakage alsoupstream of the respective ELV valve, when the valve is open and thepressure in the respective EGR EL is lower than the atmosphericpressure.

Furthermore, the engine is equipped with at least one lambda sensor (λ)or with a NOx sensor on the exhaust line, through which it is possibleto measure the ratio between the (fresh) air and the fuel introduced inthe internal combustion engine E.

FIG. 1 shows more lambda sensors, since, in the embodiment shown, theyare arranged along the exhaust line, namely along the ATS, of theengine. For the present invention, at least one lambda and/or NOx sensoris enough to realize the invention.

It has to be considered that the symbol λ (lambda) indicates the lambdaor NOx sensor itself.

According to the present invention, an error λ_(err) is estimated makinga difference between the lambda measured λ_(measured) along the exhaustline by means of said λ or NOx sensor and the lambda estimated ormeasured λ_(exp) using the means for measuring or estimating thequantity of fresh air sucked {dot over (m)}_(HFM) and of fuel injected{dot over (m)}_(FUEL):

λ_(err) = λ_(measured) − λ_(exp)$\lambda_{\exp} = \frac{{\overset{.}{m}}_{HFM}/{\overset{.}{m}}_{FUEL}}{STK}$

STK represents a variable that is generally equal to 14.6 for thediesel, to 13.5 for the biodiesel, to 10.1 for the ethanol and 17.4 forthe natural gas. According to the present invention, small values ofλ_(err), lower than 10%, are to be considered as admissible. However,the treatment has to be considered as extended to the more general casesof engines that require stricter or wider operating tolerances.

When the error, namely λ_(err), exceeds a first positive thresholdλ_(err)+, it indicates that the real lambda is higher than the oneestimated by means of also the sensor HFM, since further fresh air—notcalculated—is introduced in the engine by means of the intake/EGR line.

Thus the internal combustion engine works with an excess of air withrespect to the nominal quantity set at the planning stage, and thisimplies higher NOx emissions.

As explained above, such leakage may occur between the HFM sensor andthe inlet of the supercharger C if present, or between the HFM sensorand the intake manifold IP if the engine is not supercharged, or in theportion of low-pressure recirculation duct EL or between the ELV valveand the FC duct (FIG. 2).

According to a preferred alternative embodiment of the presentinvention, when, on the contrary, the error exceeds a second negativethreshold λ_(err)−, this means that the engine is running with less airthan what was set at the planning stage, which implies a higherparticulate and/or carbon monoxide and/or unburned hydrocarbon emission.

Such condition may occur when the engine is supercharged for a leakageof the intake duct between the outlet of the supercharger C and theintake manifold IP, or between the intake manifold IP and the EGR valve(EHV), or in the low-pressure EGR line EL if the valve ELV is not closedand at the same time the pressure of the EGR line is higher than theatmospheric one.

Thus the present invention can be implemented to detect leakages thatmake the internal combustion engine work with an excess or a lack of airwith respect to the nominal value set at the planning stage.

The system according to the present invention can be adapted to detectboth types of failure, even though they are not concomitant.

At the basis of the present invention there is the calculation of theaforementioned error between the lambda measured on the exhaust line andthe lambda estimated/measured on the basis of the quantity of air andfuel entering the engine.

According to a preferred alternative embodiment of the invention boththe first positive threshold λ_(err)+ and the second negative thresholdλ_(err)− have the same absolute value and preferably comprised between0.1 and 0.3 with an optimal value of 0.2. Such values are not binding,but are connected to the current state of the art and to the regulationson emissions in force, and thus the treatment has to be considered asextended to wider or stricter tolerance values.

According to a preferred alternative embodiment of the invention,between the outlet of the turbine and the inlet of the low-pressure EGRduct EL, a device for the reduction of pollutant emissions, such as aDPF (Diesel Particulate Filter) and/or un SCR (Selective CatalyticReduction) or, as an alternative to the SCR, a NSC (NOx storagecatalyst) may be arranged.

In order to keep the present method reliable it is preferable that theinhibition means thereof are activated as soon as heating strategies ofthe ATS and/or regeneration strategies of the DPF are activated.

Anyway it is preferable that the lambda or NOx sensor is arrangedupstream of the ATS so that it is not affected by possible variations inthe oxygen content it can introduce. A comparison between the presentinvention and US20120143459 will now be presented.

‘US20120143459 describes a method wherein a parameter Leak_Air iscalculated on the basis of the ratio between the air/fuel ratio measuredand the lambda value measured at the exhaust λ_(measured) and it iscompared with an arbitrary threshold Leak_Air_Det: the error is detectedif Leak_Air>Leak_Air_Det occurs regularly, or if in average in a certaintime interval Leak_Air>Leak_Air_Inter, the latter being generallydifferent from Leak_Air_Det. As a consequence of the aforementionedformula, the method proposed by US20120143459 can be effective only inpredicting leakages resulting in a gas leak (air or air and recirculatedexhaust gas) towards the outside, such as for example in the segment ofthe air/EGR intake line downstream of the supercharger, namely with ahigh pressure, or in the segment of the low-pressure EGR line EL whenthe low-pressure EGR valve is not closed and in such segment there arepressure conditions higher then the atmospheric pressure. On thecontrary, it generally cannot predict leakages resulting in an intake ofair from outside, such as for example in the segment of the air/EGRintake line comprised between the mass flow sensor (HFM) and thesupercharger C or on the low-pressure EGR line EL, see FIG. 2.

The air/fuel ratio is determined according to the quantity of airmeasured at the intake divided by the fuel injected and by an “air/fuelratio theoretical value” see paragraph

For a more convenient comparison, for the air fuel ratio calculatedaccording to US20120143459, the same symbol used according to thepresent invention λ_(exp) is used. Leak_Air is thus equal toλ_(measured)/λ_(exp).

According to the present invention there is no failure/leakage to besignalled when λ_(err)=λ_(measured)−λ_(exp)≅0, namely it is comprisedbetween the threshold λ_(err)− and λ_(err)+ and vice versa, there is afailure/leakage to be signalled when said error is not comprised betweenthe aforementioned thresholds.

When measured λ_(measured)≅λ_(exp), then there is not leakage andLeak_Air should be approximately equal to 1.

An λ_(err)<0 according to the present invention implies that Leak_Air>1and, analogously, an error λ_(err)>0 according to the present inventionimplies 0<Leak_air<1.

US20120143459 gives no indication about the value of Leak_Air_Det, thusit is possible to choose any value −∞<Leak_Air_Det<1, for exampleLeak_air_Det=0.8, in this way the method would detect a leakage also inabsence of real leakages/failures with Leak_air=1, namely in the case inwhich, according to the present invention, the expected lambda coincidesexactly with the measured lambda.

Thus the teaching of US20120143459 is at least incomplete.

According to another alternative embodiment of the invention, the intakeline between the outlet of the supercharger and the intake manifold IPmay comprise an intercooler CO (FIG. 1). Analogously, each one of therecirculation ducts may comprise a cooler of the recirculated gas.

Thus, according to the present invention, it is possible to detectpossible leakages by means of such coolers.

The system as described above allows to actuate a control of thecontinuous type of the sealing conditions both of the low-pressure EGRduct and of the intake line.

Such monitoring can be performed by a vehicular control unit or by theengine control unit ECU. Thus, the present invention may advantageouslybe realized by means of a computer program, which comprises program codemeans performing one or more steps of said method, when said program isrun on a computer. For this reason the scope of the present patent ismeant to cover also said computer program and the computer-readablemeans that comprise a recorded message, such computer-readable meanscomprising the program code means for performing one or more steps ofsuch method, when such program is run on a computer.

It will be apparent to the person skilled in the art that otheralternative and equivalent embodiments of the invention can be conceivedand reduced to practice without departing from the scope of theinvention.

For example, the detection of one of the possible types of failures maydetermine the signalling of an anomaly by means of a light on thedashboard of the vehicle and/or may determine the activation of arecovery procedure which limits the maximum torque and/or the maximumpower that can be delivered by the internal combustion engine E or themaximum speed of the vehicle where the present invention is implemented.

From the description set forth above it will be possible for the personskilled in the art to embody the invention with no need of describingfurther construction details. The elements and the characteristicsdescribed in the different preferred embodiments may be combined withoutdeparting from the scope of the present application. What is describedin the description of the prior art, if not explicitly excluded in thedetailed description, has to be considered in combination with thecharacteristics of the present invention, forming an integral part ofthe present invention.

1. A system for detecting a leakage/failure in an intake line of aninternal combustion engine comprising an intake line (IL) and an exhaustline (EL), means (HFM) for measuring or for estimating a quantity offresh air ({dot over (m)}_(HFM)) entering said intake line (IL), meansfor measuring or for estimating a quantity of fuel ({dot over(m)}_(FUEL)) injected into the engine (HFM), measurement or estimationmeans (λ and/or NOx), on said exhaust line, adapted to provide a firstvalue (λ_(measured)) of an air/fuel ratio introduced in the internalcombustion engine (E), the system comprising processing means (ECU)configured to calculate a second value (λ_(exp)) of said air/fuel ratio,calculated on the basis of said measured or estimated quantities offresh air ({dot over (m)}_(HFM)) and fuel ({dot over (m)}_(FUEL))injected into the engine (E), to calculate an error (λ_(err)) as thedifference between said first and second value of air/fuel ratio(λ_(measured)−λ_(exp)) and to detect a condition of leakage/failure ifsaid error is outside a predefined interval [λ_(err)−, λ_(err)+]containing the value zero.
 2. System according to claim 1, wherein whensaid engine is supercharged by means of a supercharger (C) and possiblycomprises low-pressure and/or high-pressure recirculation means, whensaid (λ_(err)) exceeds positively said predefined interval [λ_(err)−,λ_(err)+], said processing means (ECU) are configured to generate awarning message indicating a leakage in a duct comprised between saidmeans for measuring or estimating a quantity of fresh air ({dot over(m)}_(HFM)) entering the engine (E) and an inlet of said supercharger(C) and/or a leakage in a portion of a low-pressure recirculation EGRduct (EL) or in a portion of duct comprised between a respectivelow-pressure EGR valve (ELV) and said inlet of said supercharger (C); orwhen said error (λ_(err)) exceeds negatively said predefined interval([λ_(err)−, λ_(err)+]), processing means (ECU) are adapted to generate awarning message indicating a leakage in a duct comprised between anoutlet of said supercharger (C) and said intake manifold (IP) and/or aleakage in a high-pressure recirculation EGR duct comprised between arespective EGR valve (EHV) and said intake manifold (IP) and/or aleakage in a low-pressure EGR line (EL) when a respective EGR valve(ELV) is not completely closed and at the same time the EGR line is at apressure higher than the atmospheric pressure.
 3. System according toclaim 1, wherein said engine is not supercharged and possibly comprisesrecirculation means EGR, when said error (λ_(err)) exceeds positivelysaid predefined interval ([λ_(err)−, λ_(err)+]), said processing means(ECU) are adapted to generate a warning message indicating a leakage ina duct comprised between said means for measuring or estimating aquantity of fresh air ({dot over (m)}_(HFM)) entering the engine (E) andsaid intake manifold and/or a leakage in a portion of a low-pressurerecirculation EGR duct (EL) or in a portion of duct comprised between arespective low-pressure EGR valve (ELV) and intake manifold (IP); orwhen said error (λ_(err)) exceeds negatively said predefined interval([λ_(err)−, λ_(err)+]), said processing means (ECU) are adapted togenerate a warning message indicating a leakage in a low-pressure EGRline (EL) when a respective low-pressure EGR valve (ELV) is not closedand the EGR line is at a pressure higher than the atmospheric pressure.4. System according to claim 1, wherein λ_(err)− and λ_(err)+ have anabsolute value comprised between 0.1 and 0.3, so that, in a “normal”condition, wherein there is no leakage/failure,λ_(err)−<λ_(err)<λ_(err)+ results.
 5. System according to claim 4,wherein said thresholds λ_(err)− and λ_(err)+ have an absolute valueequal to 0.2.
 6. Internal combustion engine (E), having an intake line(IL) and an exhaust line (EL), means for measuring or for estimating aquantity of fresh air ({dot over (m)}_(HFM)) entering the engine (E),means for measuring or for estimating a quantity of fuel ({dot over(m)}_(FUEL)) injected into the engine (E), measurement or estimationmeans (λ and/or NOx), on said exhaust line, adapted to provide a firstvalue (λ_(measured)) of an air/fuel ratio introduced in the engine (E),the system comprising processing means (ECU) interfaced with saidmeasurement or estimation means (HFM, IS, λ e/o NOx) and adapted tocalculate a second value (λ_(exp)) of said air/fuel ratio, calculated onthe basis of said measured or estimated quantities of fresh air ({dotover (m)}_(HFM)) and fuel ({dot over (m)}_(FUEL)) to calculate an error(λ_(err)) between said first and second value of air/fuel ratio(λ_(measured)−λ_(exp)) and to detect a condition of leakage/failure ifsaid error is outside a predefined interval [λ_(err)−, λ_(err)+]containing the value zero.
 7. Engine according to claim 6, furthercomprising a supercharger (C) arranged on said intake line (IL) andpossibly low-pressure and/or high-pressure recirculation means EGR, andwherein said processing means are configured to detect a leakage/failurewhen said error (λ_(err)) exceeds positively said predefined interval[λ_(err)−, λ_(err)+], indicating a leakage in a duct comprised betweensaid means for measuring or estimating a quantity of fresh air ({dotover (m)}_(HFM)) entering the engine (E) and an inlet of said compressor(C) and/or a leakage in a portion of a low-pressure recirculation EGRduct (EL) or in a portion of duct comprised between a respectivelow-pressure EGR valve (ELV) and said inlet of said supercharger (C); orwhen said error (λ_(err)) exceeds negatively said predefined interval[λ_(err)−. λ_(err)+], indicating a leakage in a duct comprised betweenan outlet of said supercharger (C) and said intake manifold (IP) and/ora leakage in a high-pressure recirculation EGR duct comprised between arespective EGR valve (EHV) and said intake manifold (IP) and/or aleakage in a low-pressure EGR line (EL) when a respective EGR valve(ELV) is not completely closed and at the same time the EGR line is at apressure higher than the atmospheric pressure.
 8. Engine according toclaim 6, being of the type non supercharged and possibly comprisingrecirculation means EGR, and wherein said processing means areconfigured to detect a leakage/failure when said error (λ_(err)) exceedspositively said predefined interval [λ_(err)−, λ_(err)+], saidprocessing means (ECU) are adapted to generate a warning messageindicating a leakage in a duct comprised between said means (HFM) formeasuring or estimating a quantity of fresh air ({dot over (m)}_(HFM))entering the engine (E) and said intake manifold (IP) and/or a leakagein a portion of a low-pressure recirculation EGR duct (EL) or in aportion of duct comprised between a respective low-pressure EGR valve(ELV) and intake manifold (IP); or when said error (λ_(err)) exceedsnegatively said predefined interval [λ_(err)−, λ_(err)+], saidprocessing means (ECU) are adapted to generate a warning messageindicating a leakage in a low-pressure EGR line (EL) when a respectivelow-pressure EGR valve (ELV) is not closed and the EGR line is at apressure higher than the atmospheric pressure.
 9. Engine according toclaim 6, wherein λ_(err)− and λ_(err)+ have an absolute value comprisedbetween 0.1 and 0.3, so that, in a “normal” condition, wherein there isno leakage/failure, λ_(err)−<λ_(err)<λ_(err)+ results.
 10. Engineaccording to claim 9, wherein said thresholds have an absolute valueequal to 0.2.
 11. Engine according to claim 6, further comprising anintercooler (C) on the intake line (IL) and/or a cooler on arecirculation duct EGR.
 12. Engine according to claim 6, furthercomprising an anti-pollution device (DPF, SCR, NSC) on the exhaust line(EL).
 13. Vehicle or fixed apparatus, comprising an internal combustionengine having an intake line (IL) and an exhaust line (EL), means formeasuring or for estimating a quantity of fresh air ({dot over(m)}_(HFM)) entering the engine (E), means for measuring or forestimating a quantity of fuel ({dot over (m)}_(FUEL)) injected into theengine (E), measurement or estimation means (λ and/or NOx), on saidexhaust line, adapted to provide a first value (λ_(measured)) of anair/fuel ratio introduced in the engine (E), the system comprisingprocessing means (ECU) interfaced with said measurement or estimationmeans (HFM, IS, λ e/o NOx) and adapted to calculate a second value(λ_(exp)) of said air/fuel ratio, calculated on the basis of saidmeasured or estimated quantities of fresh air ({dot over (m)}_(HFM)) andfuel ({dot over (m)}_(FUEL)), to calculate an error (λ_(err)) betweensaid first and second value of air/fuel ratio (λ_(measured)−λ_(exp)) andto detect a condition of leakage/failure if said error is outside apredefined interval [λ_(err)−, λ_(err)+] containing the value zero. 14.Method for detecting a leakage in an intake line (IL) of an internalcombustion engine comprising an intake line (IL) and an exhaust line(EL), means (HFM) for measuring or for estimating a quantity of freshair ({dot over (m)}_(HFM)) entering said intake line (IL), means formeasuring or for estimating a quantity of fuel ({dot over (m)}_(FUEL))injected into the engine (E), measurement or estimation means (λ and/orNOx), on said exhaust line, the method comprising the steps of:calculation of a first value (λ_(measured)) of a air/fuel ratiointroduced in the engine (E) through said measurement or estimationmeans (λ and/or NOx) on said exhaust line calculating a second value(λ_(exp)) of air/fuel ratio entering the engine on the basis of saidmeasured or estimated quantities of fresh air ({dot over (m)}_(HFM)) andfuel ({dot over (m)}_(FUEL)) entering the engine and calculating anerror (λ_(err)) making the difference between said first value and saidsecond value (λ_(measured)−λ_(exp)) and detecting a condition ofleakage/failure if said error (λ_(err)) is outside said predefinedinterval [λ_(err)−, λ_(err)+] containing the value zero.
 15. Methodaccording to claim 14, wherein said engine is supercharged by means of asupercharger (C) arranged on said intake line (IL) and possibly providedwith low-pressure and/or high-pressure recirculation means EGR, themethod comprising a step of signalling a leakage/failure when said error(λ_(err)) exceeds positively said predefined interval [λ_(err)−,λ_(err)+], indicating a leakage in a duct comprised between said meansfor measuring or estimating a quantity of fresh air ({dot over(m)}_(HFM)) entering the engine (E) and an inlet of said compressor (C)and/or a leakage in a portion of a low-pressure recirculation EGR duct(EL) or in a portion of duct comprised between a respective low-pressureEGR valve (ELV) and said inlet of said supercharger (C); or when saiderror (λ_(err)) exceeds negatively said predefined interval [λ_(err)−,λ_(err)+], indicating a leakage in a duct comprised between an outlet ofsaid supercharger (C) and said intake manifold (IP) and/or a leakage ina high-pressure recirculation EGR duct comprised between a respectiveEGR valve (EHV) and said intake manifold (IP) and/or a leakage in alow-pressure EGR line (EL) when a respective EGR valve (ELV) is notcompletely closed and at the same time the EGR line is at a pressurehigher than the atmospheric pressure.
 16. Method according to claim 14,wherein said engine is not supercharged and possibly comprisesrecirculation means EGR, the method comprising a step of signalling aleakage/failure when said error (λ_(err)) exceeds positively saidpredefined interval [λ_(err)−, λ_(err)+], indicating a leakage in a ductcomprised between said means for measuring or estimating a quantity offresh air ({dot over (m)}_(HFM)) entering the engine (E) and said intakemanifold and/or a leakage in a portion of a low-pressure recirculationEGR duct (EL) or in a portion of duct comprised between a respectivelow-pressure EGR valve (ELV) and said inlet of said supercharger (C); orwhen said error (λ_(err)) exceeds negatively said predefined interval[λ_(err)−, λ_(err)+], indicating a leakage in a low-pressure EGR line ELwhen the valve ELV is not closed and at the same time the EGR line is ata pressure higher than the atmospheric pressure.
 17. Method according toclaim 14, wherein λ_(err)− and λ_(err)+ have an absolute value comprisedbetween 0.1 and 0.3, so that, in a “normal” condition, wherein there isno leakage/failure, λ_(err)<λ_(err)<λ_(err)+ results.
 18. Methodaccording to claim 17, wherein said thresholds λ_(err)− and λ_(err)+have an absolute value equal to 0.2.